Non-sulfided Ni-based hydrocracking catalysts

ABSTRACT

The invention provides a method for reducing methane formation when hydrocracking hydrocarbons, and a process for the hydrocracking of hydrocarbons, said method and process utilising a non-sulfided hydrocracking catalyst, which catalyst has Ni and Sn, wherein the Ni content is at least 1 mass % and the silica content is at least 20 mass %, present in the form of silica-alumina.

FIELD

The invention relates to hydrocracking catalysts.

BACKGROUND

The Low-Temperature Fischer-Tropsch (LTFT) process includes within itsprimary products a significant volume of heavy hydrocarbons,collectively referred to as waxes. Conventionally, these waxes, whichare essentially free of sulfur, are hydroconverted via hydrocrackingreactions to distillates.

As indicated by J Scherzer and A J Gruia in “Hydrocracking Science andTechnology” (Marcel Dekker, 1996), commonly used commercialhydrocracking catalysts are those based on NiW, NiMo and CoMo onamorphous silica-alumina systems. All these catalysts demand thecontinuous addition of a sulfur-containing species in order to maintaintheir performance.

The use of amorphous silica-alumina as support may produce higherselectivities to distillates, this being a consequence of its lower acidstrength, in contrast to that found in the strongly acidic zeoliticsupports (Calemma et al., Studies in Surface Science and Catalysis, 136(2001) 302).

Through the use of such hydrocracking processes, the advantage ofstarting with a sulfur-free feed and finishing with a sulfur-freeproduct will be lost, and at the same time, H₂S will be present in thetail gas. Most importantly, however, it will be highly advantageous interms of the process economics to develop a non-sulfided non-noble metalcatalyst.

Ciapetta and Hunter, in Industrial Engineering and Chemistry, 45 (1953)147, reported on the use of a non-sulfided Ni/SiO₂—Al₂O₃ catalyst forthe hydrocracking of n-hexane and n-octane. It is, however, well knownin the technical literature (see for example Lugstein et al. in AppliedCatalysis A: General, 152 (1997) 93), that supported Ni catalystsexhibit high hydrogenolysis activities, resulting in the production ofmethane, an undesirable low-value product in most cases. Thisobservation applies to Ni supported on all the commonly used supportssuch as silica, alumina, silica-alumina, zeolites, and even basicsupports, e.g. magnesium oxide. Moreover, formation of methane has to beminimized since it influences the hydrogen partial pressure in ahydrocracker operating in a gas recycle mode.

Due to commercial reasons, in the conversion of valuablecarbon-containing species, it is also desirable to minimize theconsumption of hydrogen in the production of the less valuable product,viz. methane.

From the above, it can be gathered that a need exists for a non-sulfidednon-noble metal F-T wax hydrocracking catalyst of low hydrogenolysisactivity.

SUMMARY

Surprisingly, the inventors have found a workable formulation for anactive and selective non-sulfided Ni-based catalyst of lowhydrogenolysis activity and long lifetime (avoidance of loss of thedehydrogenation/hydrogenation activity due to metal sintering etc),whereas the technical literature pertains predominantly to non-sulfidednoble metal or sulfided NiW, CoMo or NiMo on zeolitic or non-zeoliticacidic supports.

According to one aspect of the invention, there is provided ahydrocracking catalyst, which catalyst is non-sulphided and has a Nicontent of at least 1 mass % and a silica content of at least 20 mass %.

The catalyst may have a Ni content of at least 3 mass %.

The catalyst may have a Ni content of at least 4.5 mass %.

The catalyst may have a Ni content of up to 50 mass %.

In some embodiments, the Ni content is between 5 mass % and 12 mass %,typically in the range 6 mass % to 10 mass %.

The catalyst may have at least 40 mass % silica.

The catalyst may include in excess of 60 mass % silica, and even in theregion of 80 mass % silica, or even up to 99 mass % silica.

The silica may be present in the form of silica-alumina.

The catalyst may include Sn.

The catalyst may include more Ni than Sn.

Typically, the catalyst may include Ni and Sn wherein the Ni:Sn molarratio exceeds 1:1.

The Ni:Sn molar ratio may exceed 2:1, 3:1, or even higher.

In one embodiment the Ni:Sn molar ratio is 6:1.

According to another aspect of the invention, there is provided a methodfor reducing methane formation when hydrocracking hydrocarbons in thepresence of a non-sulphided Ni containing catalyst.

The catalyst may contain Sn.

The silica may be present in the form of silica-alumina.

The method may reduce the selectivity to methane to below 0.13 mass %,typically to 0.011 mass % or less, and even to 0.008 mass % or less.

The method may include including Sn in a quantity such that the molarratio of Ni:Sn is in excess of 1:1.

The method may include including Sn in a quantity such that the molarratio of Ni:Sn is in excess of 5:1.

The method may include using a catalyst which has in excess of 3 mass %Ni, typically in excess of 4.5 mass % Ni, preferably in excess of 5 mass% Ni.

The method may include using silica-alumina as the support for thecatalyst.

According to a further aspect of the invention, there is provided aprocess for the hydrocracking of hydrocarbons, said process includingexposing said hydrocarbons, for example paraffinic hydrocarbons boilingin the 370° C.+ range, also referred to as waxes, or primary F-T derivedwaxes, to a catalyst as described above in a reactor operating athydrocracking temperatures and pressures.

The process may also be used for the hydroconversion of lower boilinghydrocarbons, such as naphtha or middle distillates derived from an F-Tprocess.

The process may be performed in the temperature range of 200-450° C., ata pressure of 5-250 bar, and a Weight Hourly Space Velocity (WHSV) rangeof 0.1-10 h-¹.

The nickel-tin (NiSn) catalyst may also be used in a process for thehydrocracking of crude oil fractions, bio-mass, and in general, anysource of available hydrocarbonaceous material.

The formation of methane may be reduced by using the non-sulfidedNi-based hydrocracking catalyst to less than 1 mass %, typically lessthan 0.1 mass %.

With the use of Sn in the catalyst, the methane formation may be reducedto less than 0.03 mass %, preferably to less than 0.01 mass %.

The silica may be present in the form of silica-alumina.

The methane formation, or methane yield, is calculated as theselectivity multiplied by the fractional conversion.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 shows the effect of Ni loading on carbon number distribution;

FIG. 2 shows the product distributions obtained in the hydrocracking ofn-tetradecane over the 7% Ni and the 7% Ni, 4.7% Sn/silicated aluminacatalysts;

FIG. 3 shows the product distributions obtained at ˜28% conversion overthe 5% Ni, 1.7% Sn/silicated alumina catalysts at different timeson-stream;

FIG. 4 shows product distributions obtained over the NiSn/silica-aluminacatalysts at ˜41% conversion as a function of TOS; and

FIG. 5 shows the product distributions obtained at different metalloadings and at ˜42% conversion.

A series of Ni-based catalysts was synthesized using a commercialsilicated alumina having a silica content of 40 mass %.

The 3 and 4.5% Ni/silicated alumina samples were prepared by wetimpregnation using aqueous solutions of nickel nitrate of theappropriate concentration to give the desired metal loading. Thesesamples were tested as catalysts for the hydrocracking of n-hexadecane,which was used as the model compound. The product distributions obtainedover these catalysts, which were non-sulfided, appeared symmetrical, andwere close to ideal hydrocracking, as defined by J Weitkamp and S Ernstin “Guidelines for Mastering the Properties of Molecular Sieves”, PlenumPress, 1990, p. 343. In the hydrocracking of heavier hydrocarbons, suchas F-T waxes, ideal hydrocracking implies that the desired distillatesselectivity will be at its theoretical maximum. The results obtained,therefore, are positive indicators that non-sulfided Ni is a suitablemetal in serving as the dehydrogenation/hydrogenation function inhydrocracking catalysts. However, it was also observed that the amountof methane produced was significant.

A number of patents dealing with supported sulfided nickel-tinhydrocracking catalysts were granted to the Chevron Research Company inthe period of 1968-1970 (U.S. Pat. No. 3,399,132 (1968), U.S. Pat. No.3,542,696 (1970), and U.S. Pat. No. 3,598,724 (1971)). The objective oftin addition to the nickel catalysts was, as indicated in these patents,to increase the activity of the catalysts. However, the influence of tinon hydrogenolysis was never noted since sulfiding completely eliminateshydrogenolysis.

The inventors prepared a series of Sn-containing Ni-based catalysts foruse in hydrocracking. A NiSn/silicated alumina sample was prepared viathe co-impregnation of a Sn compound using the molar ratio of Ni:Sn=3:1.This supported NiSn catalyst was then tested for the hydrocracking ofn-tetradecane.

The catalyst without Sn (i.e. the 7% Ni/silicated alumina) produced botha highly symmetrical hydrocracking product distribution as well as asignificant quantity of methane, about 20 mole %. It was surprisinglyfound, however, that the addition of the Sn to the silicatedalumina-supported Ni-based hydrocracking catalyst resulted in the almosttotal elimination of the hydrogenolysis activity of the catalyst (theseresults are shown in FIG. 2 in Example 2). Such an observation has notbeen made previously in the patent or open literature on non-sulfidedNi-based hydrocracking catalysts.

From the above experiments it appears, therefore, that we have been ableto overcome the problem of hydrogenolysis by the addition of tin to thenickel-based hydrocracking catalysts. A problem found with the Ni orNiSn/silicated alumina catalysts, however, was the stability of thecatalyst with time-on-stream (TOS), namely, the loss of metal functionand the shift to lighter products. While initially in the run almostideal hydrocracking was obtained, after several days on-stream, a shiftto lighter products was observed. These observations are demonstrated inExample 3.

From comparative Temperature-Programmed Reduction studies of nickeloxide supported on reference supports such as silica, alumina andsilica-alumina, it was concluded that in the silicated alumina-supportednickel catalyst precursors, the nickel oxide is preferentiallyassociated with the alumina phase. Since the loss of metal functioncould be a consequence of this association, we focused our attention oncommercial silica-alumina samples which had to have a low content ofalumina (typically used as binder), a high silica content but also ahigh tetrahedral aluminium content in the silica-alumina phase in orderto possess high Brønsted acidity. As these catalyst properties are notobtainable from the manufacturers, a catalytic test reaction(dehydration of 1-hexanol) was used to ascertain the acidic activity ofthe silica-alumina extrudates. To achieve this, the reaction temperaturewas kept low (200° C.) in order to minimize the contribution of thealumina phase present in the silica-alumina extrudates to thedehydration activity, and thereby observe predominantly the catalyticactivity of the silica-alumina (and of its tetrahedral aluminiumcontent). To better understand the above, reference should be made toTable 1 in Example 4 which gives the dehydration results obtained withthe different commercial products.

Following the above studies, another series of Sn-containing Ni-basedcatalysts for hydrocracking was also prepared using the commercialsilica-alumina which contained 50 mass % silica (designated as SA2 inTable 1) and exhibited a high acid catalytic activity (e.g. dehydrationof the alcohol to the hexenes). The Ni content was varied from 6 to 10mass % and a 6:1 mole ratio of Ni:Sn was used. These catalysts weretested in bench-scale reactors for periods of up to 600 hours, usingagain n-tetradecane as the model compound. From the results obtained itcould readily be ascertained that the addition of Sn almost completelyeliminates the degree of hydrogenolysis (0.008 mass % selectivity tomethane). The beneficial effect of Sn addition for the suppression ofmethane formation in hydrocracking reactions is clearly evident fromthese examples as well (see results in Tables 3 and 4 in Example 5).

However, due to the inclusion of Sn, the molar distribution of thecracked products had shifted to lighter products and more Ni would haveto be added to obtain a better balance between the acid and metalfunctions and hence attain ideal hydrocracking. Also, optimization of ahydrocracking catalyst in terms of the % Ni and the Ni:Sn ratio has tobe determined for each catalyst system.

Furthermore, whereas with the catalyst prepared using the silicatedalumina as the carrier, a shift was already clearly noticeable after 300hours on-stream, the NiSn/silica-alumina catalysts were stable under thesame operating conditions and produced similar conversions and productdistributions with TOS.

It was also found with these catalysts that with increasing metalloading there was also a slight shift to higher carbon numbers in theproduct distribution.

These results clearly show that higher metal loadings are required forthis particular silica-alumina in order to obtain the appropriatebalance between the metal and acid functions.

It was also again surprisingly found that the methane formation over theNi/silica-alumina was considerably less than that obtained over theNi/silicated alumina. It can be concluded, therefore, that the higherthe silica content of the support/acidic component, the lower theselectivity to methane. These comparative and unexpected results arelisted in Table 5 of Example 5.

EXAMPLE 1

The 3 and 4.5% Ni/silicated alumina were prepared using aqueoussolutions of nickel nitrate hexahydrate (99% pure, Aldrich) of theappropriate concentration in order to achieve the indicated % metalloading (taking into account that the Loss on Ignition=13.8 mass %). Thesolvent was removed using a rotary evaporator at 50 mbar and 55° C. Thiswas followed by drying at 120° C. overnight and calcination at 300° C.for 2 hours. After loading a sample in the reactor, in-situ reductionwas carried out at 400° C. for 16 hours using hydrogen at atmosphericpressure. The samples were then tested as catalysts for thehydrocracking of n-hexadecane (n-C₁₆), which was used as the modelcompound. The reaction conditions for the 3% Ni/silicated alumina were350° C., 55 bar, WHSV=2.3 h⁻¹ and an H₂/n-C₁₆ mol ratio of ˜10, and forthe 4.5% Ni/silicated alumina were 345° C., 55 bar, WHSV=2.5 h⁻¹ and anH₂/n-C₁₆ mol ratio ˜9. The product distributions obtained at ˜41%conversion over these catalysts, which were non-sulfided, appearsymmetrical, and are therefore close to ideal hydrocracking.

EXAMPLE 2

A NiSn/silicated alumina sample was prepared via the co-impregnation ofa tin compound using the molar ratio of Ni:Sn=3:1. This sample wasprepared by dissolving 13.5 g of Ni(NO₃)₂.6H₂O and 3.5 g of SnCl₂.2H₂O(Aldrich) in 150 ml of 95% ethanol. To this solution, 40 g of thesilicated alumina support was added and the mixture was allowed to standfor 1 h at room temperature. The solvent removal and drying steps werecarried out as described in Example 1 followed by calcination at 600° C.for 3 h. After reduction at 450° C. for 16 h, this supported NiSncatalyst was then tested for the hydrocracking of n-tetradecane (n-C14)at 31 mass % conversion under the reaction conditions of 340° C., 50bar, WHSV=1.5 h⁻¹ and an H₂/n-C₁₄ mol ratio of ˜10. The productdistributions obtained over the Ni and NiSn/silicated alumina are shownin FIG. 2 which demonstrate clearly the beneficial effect of tinaddition to the nickel-based hydrocracking catalyst for the suppressionof hydrogenolysis.

EXAMPLE3

A silicated alumina-supported NiSn catalyst was also prepared containing5% Ni and 1.7% Sn by mass using the same procedure described in Example2. The catalyst precursor was calcined at 350° C. for 2 h, reduced at350° C. for 4 h, and the catalytic reactions were carried out at 343°C., 50 bar, WHSV=1.8 h⁻¹ and using an H₂/n-C₁₄ mol ratio of ˜10. Theproduct distributions obtained at 16 and 514 hours on-stream are shownin FIG. 3. The shift to lighter products with TOS due to the loss ofmetal function is clearly evident.

EXAMPLE 4

TABLE 1 The use of 1-hexanol dehydration for the evaluation of theBrønsted acidity of commercial silica-aluminas Reaction conditions: 200°C., WHSV = 3.0 h⁻¹ and TOS = 1.0 h Silica- SiO₂ products (mass %)alumina content Conversion Dihexyl Other sample (mass %) (mass %)Hexenes ether products SA1¹ 98 24.0 15.7 5.6 2.7 SA2² 50 21.2 11.2 9.30.7 SA3² 80 2.6 0.3 1.6 0.7 SA4² 50 2.7 0.6 2.1 — SA5² 22 8.0 2.0 4.91.1 γ-alumina — 8.4 0.8 3.6 3.9¹Neat silica-alumina prepared using a literature method (J Heveling, CPNicolaides and MS Scurrell, Applied Catalysis A: General, 173 (1998) 1).²Commercial silica-alumina samples.

EXAMPLE 5(a)

A second series of NiSn catalysts was prepared using the high-aciditySA2 silica-alumina as support, which had a silica content of 50 mass %.The Ni content was varied from 6 to 10 mass % and a 6:1 mol ratio ofNi:Sn was used. All samples were calcined at 350° C., and 10 ml ofcatalyst precursor diluted with 10 ml of carborundum were loaded in thereactor. Reduction was performed for 16 h at 350° C. under atmosphericpressure using a hydrogen flow of 20 l_(N)/h. Table 2 shows the basiccharacteristics of the catalysts. TABLE 2 Characteristics of theNiSn/silica-alumina catalysts Catalyst Ni (mass %) Sn (mass %) A  6.02.0 B  8.0 2.7 C 10.0 3.4 D 10.0 no tin

EXAMPLE 5(b)

The catalysts described in Example 5(a) were used for the hydrocrackingof n-tetradecane under the reaction conditions listed in Table 3. The %conversions and % methane selectivies obtained are also given in thesame Table.

The methane selectivity had decreased from about 0.13 mass % with the 7%Ni/silica-alumina sample to 0.008 mass % with the Sn-containing catalyst(see Tables 3 and 4). The beneficial effect of Sn addition for thesuppression of methane formation in hydrocracking reactions is clearlyevident from these examples as well. TABLE 3 Hydrocracking ofn-tetradecane over the catalysts of different % Ni and Sn loadings¹Catalyst A B C D pressure bar 50 50 50 50 WHSV h⁻¹ 1.7 1.6 1.7 1.9temperature ° C. 325 328 329 315 conversion mass % 69.0 72.8 72.5 71.8CH₄ selectivity mass % 0.008 0.008 0.008 0.13¹Reactions carried out in bench-scale reactors using 10 ml of catalystdiluted with 10 ml of carborundum.

EXAMPLE 5(c)

The % conversion and % selectivity to methane as a function of TOS forthe 10% Ni, 3.4% Sn/silica-alumina catalyst are listed in Table 4. Thereaction conditions were 323° C., 50 bar, and an H₂/n-C₁₄ mol ratio of˜10. The results show the stable performance of the catalyst with TOS aswell the extremely low levels of methane formation. TABLE 4 % Conversionand % methane selectivity as a function of time-on-stream for the 10%Ni, 3.4% Sn/silica-alumina catalyst Time-on-stream Conversion Methaneselectivity (hours) (mass %) (mass %)  40 45.9 0.009 136 44.0 0.007 18434.2 0.010 232 38.3 0.011 352 37.8 0.009 400 38.9 0.008 496 34.5 0.009

EXAMPLE 5(d)

The product distributions obtained at different times on-stream over thecatalyst described in Example 5(c) are shown in FIG. 4. The reactionconditions are as given in Table 3. The results show that similarproduct distributions are obtained 5with this catalyst at differenttimes on-stream and that there is clearly no shift to lighter products.

EXAMPLE 5(e)

FIG. 5 shows the product distributions obtained over the catalysts withdifferent metal loadings, as described in Table 3. It can be seen thatthere is an increasing shift to higher carbon numbers (C₆-C₁₁) withincreasing metal loading.

EXAMPLE 6

In this example, a comparison is made between the % selectivities tomethane observed in the experiments conducted using the catalystscontaining nickel only and the two different supports. The resultsclearly show that even though a higher nickel loading was used in theNi/silica-alumina catalyst, a much lower selectivity to methane wasattained. The beneficial effect of a high silica content and a lowalumina content in hydrocracking catalysts for minimizing the extent ofmethane formation (hydrogenolysis) is thus demonstrated. TABLE 5 Effectof alumina content on methane selectivity Catalyst mass % alumina mass %methane  7% Ni/silicated alumina 60 4.3 10% Ni/silica-alumina 20 0.1

1. A method for reducing methane formation when hydrocrackinghydrocarbons in the presence of a non-sulfided Ni containing catalyst,which catalyst has a Ni content of at least 1 mass % and a silicacontent of at least 20 mass %, present in the form of silica-alumina. 2.A method as claimed in claim 1, wherein the methane formation is reducedto below 1 mass %.
 3. A method as claimed in claim 2, wherein themethane formation is reduced to below 0.1 mass %.
 4. A method asclaimed, in claim 1, which has a Ni content of at least 3 mass %.
 5. Amethod as claimed in claim 1, which has a Ni content of at least 4.5mass %.
 6. A method as claimed in claim 1, which has at least 40 mass %silica.
 7. A method as claimed in claim 1, wherein the catalyst containsSn.
 8. A method as claimed in claim 7, wherein the methane formation isreduced to below 0.01 mass %.
 9. A method as claimed in claim 1, whereinthe Ni:Sn molar ratio exceeds 1:1.
 10. A method as claimed in claim 1,which method includes using silica-alumina as the support for thecatalyst.
 11. A process for the hydrocracking of hydrocarbons, saidprocess including exposing said hydrocarbons to a non-sulfided Nicontaining catalyst, which catalyst has a Ni content of at least 1 mass% and a silica content of at least 20 mass % and the silica is presentin the form of silica-alumina, in a reactor operating at hydrocrackingtemperatures and pressures.
 12. A process as claimed in claim 11,wherein the hydrocarbons are paraffinic hydrocarbons boiling in the 370°C.+ range.
 13. A process as claimed in claim 11, wherein thehydrocarbons are lower boiling paraffinic hydrocarbons.
 14. A process asclaimed in claim 11, which process is operated in the temperature rangeof 200-450° C., at a pressure of 5-250 bar, and a WHSV=0.1-10 h⁻¹.
 15. Aprocess as claimed in claim 11, which has a Ni content of at least 3mass %.
 16. A process as claimed in claim 11, which has a Ni content ofat least 4.5 mass %.
 17. A process as claimed in claim 11, which has atleast 40 mass % silica.
 18. A process as claimed in claim 11, whereinthe silica is present in the form of silica-alumina.
 19. A process asclaimed in claim 11, wherein the catalyst contains Sn.
 20. A process asclaimed in claim 11, wherein the Ni:Sn molar ratio exceeds 1:1.
 21. Aprocess as claimed in claim 11, which method includes usingsilica-alumina as the support for the catalyst.
 22. A catalyst for usein a method for reducing methane formation when hydrocrackinghydrocarbons, said catalyst being non-sulfided and containing Ni andsilica, wherein the Ni content is at least 1 mass % and the silicacontent is at least 20 mass % and the silica is present in the form ofsilica-alumina.
 23. A catalyst as claimed in claim 22, which has a Nicontent of at least 3 mass %.
 24. A catalyst as claimed in claim 22,which has a Ni content of at least 4.5 mass %.
 25. A catalyst as claimedin claim 22, which has at least 40 mass % silica.
 26. A catalyst asclaimed in claim 22, which catalyst contains Sn.
 27. A catalyst asclaimed in claim 22, wherein the Ni:Sn molar ratio exceeds 1:1.
 28. Acatalyst as claimed in claim 22, which method includes usingsilica-alumina as the support for the catalyst.